A major goal of HIV-1 research is the development of nontoxic agents that target novel stages of the viral replicative cycle. Such agents are needed both to combat the growing incidence of HIV-1 strains that are broadly resistant to existing antiretroviral medications and to lessen the considerable toxicities associated with current therapies. In addition, since adequate control of HIV-1 replication has generally required the chronic use of three or more drugs in combination, it becomes imperative that new antiretrovirals are produced as cost-effectively as possible. CD4-IgG2 is a novel HIV-1 entry inhibitor that incorporates four copies of the virus binding domains of human CD4 into a tetravalent antibody-like molecule. CD4-IgG2 has demonstrated potent activity against primary HIV- 1 isolates in extensive preclinical testing and more recently in Phase I/II human clinical trials. CD4-IgG2 is currently produced via conventional cell culture methods. However, transgenic technology provides an unsurpassed method for low-cost, high-volume manufacture of biopharmaceuticals. The goal of the Phase I project is to optimize the expression of CD4-IgG2 in the milk of transgenic animals, using mice as a model system. In the Phase II project, the optimized methods will be used to create transgenic dairy animals for highly cost-effective production of late-stage clinical and commercial supplies of CD4-IgG2. PROPOSED COMMERCIAL APPLICATIONS: This project seeks to develop cost-effective methods for producing a promising new anti-HIV-1 agent. For a drug that safely and effectively blocks an early, previously untargeted step of the HIV-1 replicative cycle, the market would be HIV-infected individuals who are suboptimally treated by existing therapies. These individuals include those with measurable viral loads despite highly active antiretroviral therapy and those who experience significant treatment toxicities. Currently, these individuals comprise a sizeable if not majority fraction of HIV-infected individuals, who number approximately 900,000 in the U.S. This agent may also find additional application in preventing HIV-1 infection following occupational or perinatal exposure. Cost-effective production methods will improve patient access to the drug as well as maximize its potential applications.